This invention relates to a method and an apparatus for converting monoscopic (i.e., two-dimensional) images into stereoscopic (i.e., three-dimensional) images, and more particularly using image warping.
The human brain perceives depth by receiving two different images, which are horizontally shifted relative to each other, from each eye. Such depth information is important for determining how far away an object is and the depth arrangements between various objects in a scene. Unfortunately, most images are recorded in monoscopic format on recording medium (e.g., motion picture film and video media) where some depth information is lost. However, even a monoscopic camera lens produces an image according to the laws of Cartesian space and perspective. If such an image could be processed to extract that information, and thus be converted into three-dimensional stereoscopic format, there could be a vast amount of stereoscopic material available for three-dimensional viewing.
There are several methods to generate stereoscopic images from monoscopic images. One method, the horizontal shift method, isolates several important objects in the image field and shifts them horizontally. B. J. Garcia, Ph.D. and R. J. Greenstein, M.D., "True-Stereoscopic Video Media from Monoscopic Sources: The DeepVision System for Minimally Invasive Surgery," Medical Applications, Virtual Reality Systems, pp. 52-57 (1994). The amount of the shift for each object varies according to its depth arrangement. The depth arrangement (also referred to as stereoscopic depth cue or binocular disparity) of an object can be set manually using cues such as shadows and the perspective within the monoscopic image. This process creates a stereoscopic image with depth perception between objects, but the objects themselves lack depth and appear to be flat cardboard cutouts.
Another method, the frame delay method, uses moving images to extract a second perspective. H. Murata, T. Okino, T. Iinuma, S. Yamashita, S. Tanase, K. Terada and K. Kanatani, "Conversion of Two-Dimensional Images to Three Dimensions," SID 95 Digest, Society for Information Display 1995 Symposium Proceedings (1995). When an object is in motion, a series of different perspectives is generated due to either the object's movement or the camera's motion. Different perspectives from different images in a time series can then be extracted to generate a second perspective for the stereoscopic effect. Though this technique can create very realistic three-dimensional effects, it requires that motion of both the camera and the objects be limited to a direction horizontal to the image frame's horizontal axis. The camera must move in a horizontal fashion perpendicular to the subject matter (this is called a "truck" in the motion picture industry). The reason for this perpendicular motion is that each stereoscopic image pair is formed by pairing up images which are delayed from each other. Because the camera is limited to sideways motion, the delay between images results in a parallel camera separation. If the camera were not moving in a perpendicular and horizontal manner, the image pairs would not be parallel and would not form a good stereoscopic image. Also, since this technique requires a series of images taken at different times, a single image cannot be converted.
In view of the foregoing, it would be desirable to be able to provide a method and an apparatus for converting monoscopic images into stereoscopic images which gives the appearance of depth to objects themselves, as well as the appearance of depth between objects. It would also be desirable to be able to convert images with vertical as well as horizontal object motion relative to the frame's horizontal axis. It would also be desirable to be able to convert a single image.